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Socket Set Screws

Banner illustrating the different Set Screw point styles including cup point and knurled point set screws.

Set screws are used to fasten an object inside or against another object, such as attaching a gear to a shaft. In other words, rather than binding materials together via threads, a set screw applies pressure at the tip to anchor objects in a set position. Socket set screws are available with several different point styles each with its own pros and cons. Set screws are available in a full range of both inch and metric sizes in standard or bulk packaging. Using the filters to the left, you can search via point style, length, diameter-thread size, material, finish or feature. Click HERE for additional technical information including: head dimensions, thread & body dimensions, mechanical requirements and nominal screw length. And as always, contact us should you need help finding the correct grub screw for your project. We're here to help!

Choosing a Socket Set Screw

Socket Set Screw Head Styles

Socket set screws, or grub screws, feature a headless (or blind) design, meaning that no head projects past the major diameter of the screw thread. They are driven with an internal-wrenching drive, most commonly a square or hex key. Conversely, square head set screws feature an external square head that enables wrench tightening even in confined spaces.

Socket Set Screw Point Styles

Cup point set screws feature a hex drive at one end and a cup-shaped indentation at the other. The most commonly used head style, the thin edge of the cup end digs into the contact surface for high holding power. It is useful for fast permanent and semi-permanent placement in applications where some indentation left by the cup end is acceptable.

Knurled cup set screws feature one slight variation from the cup point set screw. This style has serrated ridges, or knurls, in the indented cup that bite into the contact material and effectively lock in place for a powerful grip that resists loosening caused by vibration. As with the cup point, a certain amount of scaring on the surface of the contact material is likely. Knurled set screws should not be re-used because the knurled ridges suffer damage upon removal and therefore offer less strength upon re-setting.

Also known as extended point set screws, dog point and half-dog point set screws feature a protruding tip with a flat surface on the end that opposes the hex drive. This protrusion is longer on the full dog set screw than on its half dog point relative. Designed for permanent setting, the protrusion should fit into a matching hole in the workpiece much as a dowel pin would.

Oval point socket set screws have a rounded, oval-shaped point that causes minimal surface damage at the contact site when installed. The minimal contact area allows the user to make slight adjustments without loosening the screw.

Flat point set screws possess a flat surface at the end opposite the hex socket drive. Surface damage caused by this point style is minimal because the blunt tip does not dig in at the contact point making the flat point the desired choice when minimal surface scaring is desired and for applications where frequent re-setting and relocation is necessary. Grounding the flat improves the grip at the contact point.

Cone point set screws have a sharp, cone-shaped point that wedges into the contact material thus delivering the strongest torsional and axial holding power of all the set screw styles. They are most often utilized in permanent settings, though they can also be used as a pivot or hanger.

Socket Set Screw Materials

The majority of socket set screws are manufactured from steel or alloy steel with a minimum Rockwell hardness of C45. Steel set screws are strong, but not very resistant to corrosion though applied coatings or finishes can enhance their corrosion resistance. Nickel alloy set screws are good for marine and chemical-processing environments. They are strong, heat-resistant and slightly magnetic. Non-magnetic brass set screws are excellent conductors of electricity. For the maximum level of corrosion resistance, choose mildly magnetic stainless steel set screws.

Socket Set Screw Finishes

Socket set screws are typically supplied with a thermal black oxide finish which is a conversion coating that resists abrasions, reduces light glare and reflection and makes the surface of the fastener smoother. Other available finish processes include case hardened zinc, mechanical zinc, and zinc-bake Cr+3. Stainless steel set screws are left plain.

Socket Set Screw Features

Set screws, or grub screws, are available with applied nylon patches, nylon pellets and nylon tips for use when loosening from vibration is a problem. A nylon patch is a pre-applied engineered plastic threadlocking coating that is fused to the threads of the fastener. When the fastener is installed, the patch is compressed and acts like a wedge which creates a strong, self-sealing lock which stays strong even in stressful situations. A nylon pellet, or nylon plug, works in much the same way except that the threadlocking material is inserted into a pre-drilled hole in the side of the fastener. Fasteners with either nylon patches or pellets are adjustable and reusable.

Nylon tip set screws have a pre-applied pellet of nylon inserted into the set screw end. As the pellet is compressed, it performs a spring action that pushes back on the fastener and increases friction within the threads, thereby preventing the fastener from loosening. Additionally, the compressed insert acts as a barrier that prohibits marring or scaring of the contact surface.

Working on the same principle as a nylon tip, the soft, malleable end of a brass-tip set screw molds itself to the curvature of a shaft or contact surface, thus locking the fastener in place without marring the surface.

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